This invention relates to mixtures of ceramic materials and metals known as cermets and in particular, to a cermet thin-film resistor used in thermometry.
Mixtures of ceramics and metals may possess properties which are not manifest in either individual constituent. Such mixtures known as cermets are described, for example in U.S. Pat. No. 4,183,746. As set forth in that patent, one type of cermet, platinum-alumina, was identified as electrically conducting having potential utilization as a high temperature thermometer. Cermets are also reviewed in Abeles, Appl. Solid States Sci. 6,1, (1976).
In order to have a useful thermometer, the device must often meet stringent and conflicting requirements. The device should be easy to use, sensitive over a wide temperature range, stable, small, and have a low heat capacity and additionally have a weak magnetic field dependence. Most probes used for low temperature thermometry are either not monotonic in temperature, diverge faster than a power law or saturate at a limiting value. Thus, their working temperature range is limited. To date, while cermets have been the subject of exploration for a variety of different utilizations, the definition of a satisfactory cermet thermistor has not been achieved.